1. Field of the Invention
The present invention relates to injection molding machines, and in particular to adjustable die closing units for injection molding machines having a die closing unit of the knee linkage type with an axially adjustable thrust stock.
2. Description of the Prior Art
In heavy-duty injection molding machines, it is known to use die closing units of the knee linkage type which have their movable die plate supported on at least two guide spars extending between the stationary die plate and a stationary thrust stock outside the movable die plate, and where the knee linkage end points of the hydraulic drive are connected to the thrust stock and the movable die plate, respectively. Whenever a new molding die is mounted between the die plates which has a different closed height than the previously used molding die, the trust stock has to be adjusted accordingly.
It is known to obtain this adjustment by means of a worm gear drive arranged in the thrust stock, the worm being arranged on a crank-driven shaft, and the worm gear being internally threaded and seated on an externally threaded length portion of the guide spar. In the prior art device, each adjustment position is clampingly secured by means of two clamping nuts seated on the same threaded portion of the guide spar, engaging the thrust stock from the side of the molding die, the second nut serving as a counter-nut.
This prior art structure has the disadvantage that access to these clamping nuts for re-adjustment of the thrust stock position requires positioning of the die closing unit in its stretched knee linkage configuration, and that access to the clamping nuts is difficult, because a protective cover encloses the die closing unit. Prior to each adjustment of the thrust stock, it is therefore necessary to first remove this protective cover from the machine, in order to gain access to the clamping nuts.